This disclosure is intended to teach by way of example and not by way of limitation.
This disclosure relates to the field of preparation of a low-sulfate 5-sulfoisophthalic acid, mono-lithium salt from 5-sulfoisophthalic acid. In particular, this disclosure relates to the preparation of low-sulfate 5-sulfoisophthalic acid, mono-lithium salt (LiSIPA) from 5-sulfoisophthalic acid (SIPA or HSIPA) via the use of an acetic acid/water solvent mixture.
Commercially, LiSIPA is primarily used as an additive in the production of nylon carpet fiber to impart cationic dye-ability to the polymer carpet fiber. The currently utilized processes for the production and purification of LiSIPA have numerous disadvantages, including a low product yield and high manufacturing costs. Further, the resultant LiSIPA from current processes is a LiSIPA with a high sulfate level (i.e., above 200 ppm). More typically the sulfate levels in LiSIPA from known processes are from 1000 to 3000 ppm.
The high sulfate levels are the result of the known manufacturing methods employing a “water-only process” having a product precipitation step utilizing a 30% to 40% sulfuric acid (i.e., sulfate) solution.
A problem inherent to the production of such a high sulfate LiSIPA is the associated high levels of nylon filament breakage due to sulfate precipitation. Accordingly, LiSIPA with a low-sulfate composition is of value because it is expected to reduce the levels of nylon filament breakage due to sulfate precipitation, and reduce the loss of product and throughput that occurs when LiSIPA with higher sulfate levels is used.
Due to these and other problems in the prior art, some of which are disclosed herein, there is now a new process for the preparation of a low sulfate 5-sulfoisophthalic acid, mono-lithium salt from 5-sulfoisophthalic acid via the use of an acetic acid/water solvent mixture.
Liquid acetic acid is a known hydrophilic (i.e., polar) protic solvent, similar to ethanol and water. The moderate relative static permittivity (i.e., dielectric constant) of acetic acid, 6.2, allows it to dissolve not only polar compounds such as inorganic salts and sugars, but also non-polar compounds such as oils and elements such as sulfur and iodine. Acetic acid also has the ability to readily mix with other solvents, both polar and non-polar, such as water, chloroform, and hexane.
Commonly known uses of acetic acid are as a solvent for recrystllization to purify organic compounds. For example, pure acetic acid is used as a solvent in the production of terephthalic acid (“TPA”). Other uses for acetic acid are as a solvent for reactions involving carbocations, such as Friedel-Crafts alkylation and when reducing an aryl nitro-group to an aniline using palladium-on-carbon.
While acetic acid is a known solvent, it is not a solvent that has been utilized in the production and preparation of 5-sulfoisophthalic acid, mono-lithium salt (LiSIPA) or any other salt of 5-sulfoisphthalic acid (HSIPA).